Vinyl ester compositions comprising vinyl esters--such as adducts of methacrylic acid with epoxy resins--and non-resinous vinyl monomers, such as styrene, are well known. The known vinyl ester art includes the disclosures of at least the following patents, incorporated herein by reference, for all purposes which legally may be served thereby: British No. 1,030,760 and U.S. Pat. Nos. 3,066,112; 3,179,623; 3,256,226; 3,301,743; 3,317,465; 3,345,401; 3,373,221; 3,377,406; 3,432,478; 3,548,030; 3,564,074; 3,634,542; 3,637,618; 3,684,617; 4,310,644 and 4,338,242.
Vinyl ester/styrene compositions are marketed under several different trade names by as many different companies (such as "DERAKANES", by the Dow Chemical Company; "EPOCRYL" resins, by Shell Chemical Co., and "CO-REZYNS", by Interplastics Co., for example). This type of resin composition exhibits superior chemical resistance (when cured) and has excellent electrical- and thermal-insulation properties. Strong, lightweight composite structures are readily fabricated from it with glass fibers. However, although these resins generally have relatively high impact strengths, there is room for improvement in this regard. That is, for certain applications--such as corrosion-resistant liners for underground pipes, for example--greater flexibility and "toughness" are essential. Thus, the problem of modifying the resins to meet the latter requirement, while largely retaining their otherwise very adequate properties, has developed.
A substantial improvement is achieved by dissolving a carboxy-terminated, butadiene/acrylonitrile rubber (such as "CTBN"; registered trade name of B. F. Goodrich Co.) in the vinyl ester resin/styrene composition. However, this rubber is quite expensive and the amounts of it which must be added to attain even a 10% elongation are such as to adversely affect certain of the other resin properties (such as viscosity and resistance to gasoline, for example) to an undesirable extent. Consequently, a need for a more suitable flexibilizer for vinyl ester resin systems exists.
U.S. Pat. No. 4,390,662 (Ando et al; June 28, 1983; effective reference date Mar. 25, 1981) teaches toughening of polyester and vinyl ester resins (vinyl esters plus styrene) with unsaturated polyurethanes prepared by reacting 1 molecular proportion of an organic diol with from 0.7 to 1 molecular proportion of a diisocyanate and capping the resulting adduct with 2 molecular proportions of a hydroxyalkylacrylate. The Ando polyurethanes have molecular weights corresponding to "weight-average molecular chain extensions, calculated as polystyrene," of from 100 to 1500 .ANG., preferably from 200 to 1000 .ANG., most preferably from 300 to 1000 .ANG.. That is, the rectilinear length of an unstraightened polystyrene molecule having a molecular weight equal to the weight average molecular weight of the polyurethane is from 100 to 1500 .ANG., etc. A length range of from 100 to 1000 .ANG. corresponds to a moleuular weight range of from about 22,295 to about 2,229,500.
The patent teaches that in order to be an effective toughener, the polyurethane must phase out upon curing of polyester/styrene/urethane compositions but must not phase out upon curing of vinyl ester/styrene urethane compositions.
Thus, the patent teaches away from the use of oligomeric urethanes for toughening of either polyester or vinyl ester resins. It also teaches away from toughening of vinyl ester resins with urethanes which phase out upon curing.
U.S. Pat. No. 4,222,996 (Navin et al, Dec. 27, 1983; effective reference date Jan. 11, 1982) discloses in-mold coating of partially cured, molded, fiber-reinforced, thermosetting plastic articles. The coating composition has a long pot life and consists essentially of a vinyl monomer such as styrene or various acrylates--including epoxy acrylates or vinyl ester resins, and an acrylate terminated polyurethane. The urethane can constitute as much as 83 weight % of the composition and is made by reacting 1 molecular proportion of a hydroxyalkyl acrylate and from 0.15 to 0.5 molecular proportions of an organic diol with an amount of a diisocyanate which provides from 0.9 to 1 isocyanate group per hydroxyl group. Nothing is said in the patent about toughening, elongation or tensile or impact strengths. Neither is there any suggestion of preparing the main body of the article itself from resins of the nature disclosed for coatings. The only teaching from which any inference might be drawn as to phasing behavior in the cured coatings is to the effect that inclusion of an opacifier is an option. (Coating thicknesses greater than 0.004" are not suggested.)